24-Month Study Model (24MS)

Overview

The 24-Month Study Model (24MS) is one of three river system models developed and maintained by Reclamation to support operational decision-making and planning for the Colorado River Basin. All three models are implemented in the RiverWare modeling platform and share some key features, such as a monthly time-step, the same methods to estimate reservoir evaporation and bank storage, and the same current operating rules.

24MS is used for short-term (1-2 years) projections for operational decision-making, and is typically run in a deterministic mode, meaning that a single inflow scenario is used to generate a single output trace for analysis. The model is run every month to provide operational updates as inflow hydrology forecasts and demand projections evolve.

The results of the monthly runs of 24MS are formatted by Reclamation as a standardized set of data tables totaling 17 pages, known as 24-Month Study Reports. However, the Upper Colorado and Lower Colorado regional offices package and distribute this set of data tables differently; Upper Colorado adds a 9-page narrative summary for the Upper Colorado reservoirs, while Lower Colorado adds a single cover page with very a brief summary.

Figure 1. The Mid-term Probabilistic Operations Model (MTOM) in object view superimposed on a basin map, showing how the features of the Colorado River Basin are represented in the model. (Source: Reclamation)

Relevance

The 24MS projections of Lake Powell and Lake Mead levels for the coming water year determine the tier for the Annual Operating Plan and thus also the annual release volume from Lake Powell, and any reductions in delivery to the from Lake Mead to the Lower Basin states and Mexico. This fact alone means that Lower Basin stakeholders avidly follow the 24-Month Study Reports, as do many Upper Basin stakeholders as well.

Model Structure and Operation

Basically, 24MS takes a projected inflow sequence and runs it through prescribed operational rules at 12 Reclamation reservoirs to project the monthly levels and storage at those reservoirs over the next 24 months. A total of 19 inflow points are used to represent both inflows to those reservoirs and intervening flows between reservoirs.

The inflow sequences are provided by the NOAA Colorado Basin River Forecast Center (CBRFC) and are based on a blend of CBRFC's seasonal streamflow forecasts and average historical inflows, depending on (1) the month when 24MS is run, and (2) the future month that is projected.

RiverWare is an object-oriented modeling platform in which the objects may be inflow points, river reaches, diversions, reservoirs, canals, pipelines, and other water-resource features. Model

Data and Tools

Data and tools for the primary Reclamation models are listed on their respective pages:

• 24-Month Study Model (24MS)
• Mid-term Probabilistic Operations Model (MTOM)
• Colorado River Simulation System (CRSS)

Additional Resources

State of the Science Report

Chapter 3 of the State of the Science report, Primary Planning Tools, describes the three primary Reclamation system models in detail.

New and Notable Research (2020-present)

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Summary